Field of the Invention
The present invention relates to a sheet processing device that folds a sheet bundle formed by sheets that are sequentially carried out from an image forming device such as a copier or a printer and accumulated in a bundle and, more particularly, to a sheet processing device that performs processing for preventing the folded sheet bundle from being opened after discharge by pressing a fold of a folded sheet bundle while preventing damage of a sheet end portion and deviation of the folded sheet bundle from a proper position.
Description of the Related Art
There are widely known processing devices that align sheets carried out from an image forming device and staple them, or fold them into a booklet. Among them, some processing devices are configured to saddle-stitch the sheet bundle with a staple or an adhesive and fold the sheet bundle into a booklet. Such a device performs folding sheet bundle formed by 2 or 3 sheets to about 30 sheets in two; however, there may be a case where the two-folded sheet bundle is unintentionally opened after being discharged from the device, degrading aligning property of the sheet bundle, which results in reduction in accumulation amount.
Thus, as processing to cope with this problem, it is widely known that the fold of the two-folded sheet bundle that has once been subjected to folding is subjected to pressing from front and back sides thereof.
For example, as illustrated in FIG. 21, Japanese Patent No. 4,514,217 discloses a device that presses from above and below the fold of a folded sheet bundle BS by means of a pressing roller moving along the fold. The pressing roller is a pair of pressing rollers 361a and 361b. The pressing roller pair 361a and 361b are supported by a holder 362 and moved thereby along a fold direction F. With this configuration, the folded sheet is prevented from being opened after discharge.
Further, as illustrated in FIGS. 22A and 22B, Jpn. Pat. Appln. Laid-Open Publication No. 2012-201462 disclose a device in which two pressing roller pairs 461 and 463 are provided in a holder 462 that is moved along the fold of the sheet bundle. The pressing roller pair 461 is long in a sheet conveying direction and the processing roller pair 463 is short in the sheet conveying direction. In this device, depending on the number of sheets forming the sheet bundle, a position of the fold of the sheet bundle is moved forward and backward. When the number of sheets is small, the fold is pressed only by the long roller pair, and when the number of sheets is large, both the long and short pressing roller pairs 461 and 463 are used to press twice the fold. Thus, when the number of sheets is large, the fold is pressed at two positions and thereby strengthened.
As another embodiment, there is disclosed a configuration in which one of pressing roller pairs disposed in the fold direction is designed such that opposing rollers can be moved in a direction separating from each other. That is, when the number of sheets is large, the fold is pressed by the pressing roller pairs of two rows; on the other hand, when the number of sheets is small, the fold is pressed only by the pressing roller pairs of one row.
Further, as illustrated in FIGS. 23A and 23B, Jpn. Pat. Appln. Laid-Open Publication No. 2014-76903 discloses a processing device provided with a pair of pressing rollers 561a and 562a that press the fold of a two-folded sheet bundle in a sheet thickness direction and a holder 560 that reciprocates the pressing roller pair in a sheet width direction. Further, the processing device is configured to move the rollers of the pressing roller pair between a position where they are separated away from each other and a position where they are brought into pressure contact with each other. Upon re-folding the sheet bundle, the holder 560 is moved inward of the sheet bundle from an end portion thereof in the sheet width direction with the rollers of the pressing roller pair separated away from each other, as illustrated in FIG. 23A. After the holder 560 is moved inward, the rollers of the pressing roller pair are brought into pressure contact with each other to press one side of the sheet bundle. After the holder 560 passes through one end portion of the sheet bundle, the pressure contact state between the pair of pressing rollers are released to separate the rollers of the roller pair from each other and, when the holder 560 is moved toward the other side, the pressing roller pair is made to pass through the end portion of the sheet bundle in the separated state. Thereafter, the rollers of the pressing roller pair are brought into pressure contact with each other once again to press the other side of the sheet bundle. In other words, the pressing against the fold of the sheet bundle is started from the inside of the sheet bundle in the sheet width direction to the end portion thereof.
The above-described devices that perform pressing against the fold of the folded sheet bundle carried out from an image forming device or the like have the following problems.
In the device disclosed in Japanese Patent No. 4,514,217, the pair of pressing rollers 361a and 361b are moved inward from the sheet bundle end portion in the sheet width direction in the pressure contact state, so that the rollers collide with an end portion 371 of the sheet bundle, with the result that the sheet may be torn or damaged due to pressing. In addition, the collision may cause the sheet bundle to be inclined, so that a large holding mechanism is required for preventing the inclination. In particular, in this invention, a support fulcrum of the pair of pressing rollers 361a and 361b is positioned at a downstream side of the holder 362 in the moving direction, so that when the rollers collide with the end portion 371 of the sheet bundle, they are applied with a mutually approaching (closing) direction force, which increases impact on the sheet end portion.
In the device disclosed in Jpn. Pat. Appln. Laid-Open Publication No. 2012-201462, the position of the sheet bundle is changed depending on the number of sheets forming the sheet bundle BS. That is, when the number of sheets is small, the fold is pressed only by the long roller pair 461, and when the number of sheets is large, both the long and short pressing roller pairs 461 and 463 are used to press twice the fold. However, also in this case, the rollers of the pressing roller pairs 461 and 463 of respective rows are brought into pressure contact with each other, so that when, in particular, the number of sheets is large, the pressing roller pairs 461 and 463 collide with the sheet end portion, with the result that the sheet may be torn or damaged due to pressing. In addition, the collision may cause the sheet bundle to be inclined.
In the device disclosed in Jpn. Pat. Appln. Laid-Open Publication No. 2014-76903, the rollers of the pressing roller pair are separated from each other at a standby position outside the sheet bundle in the sheet width direction. Then, after being moved to the width direction inside of the sheet bundle having the fold in the separated state, the rollers of the pressing roller pair are brought into pressure contact with each other for sheet bundle pressing. When passing through the end portion in the sheet width direction, the rollers are separated from each other, making it possible to suppress the end portion of the sheet bundle from being torn or damaged due to pressing. However, the separation of the rollers is always made irrespective of whether the number of sheets is large or small, a separation mechanism is required, resulting in structural complication. In addition, every time the rollers are returned in its reciprocation, they need to pass through the end portion of the sheet bundle, irrespective of the number of sheets, so that it takes time to complete the pressing processing.